1. Field of the Invention
The present invention relates to security code identification systems for long distance telephone services and, more specifically, to an identification system using codes that are user and time dependent.
2. Prior Art
Over the past few years, a large number of long distance telephone companies have appeared to compete in the long distance telephone services market. Typically, subscribers of these services are each issued a unique seven or eight digit identification code that allows them access to a particular service. To use the service, a subscriber usually calls a local telephone number, enters that subscriber's individual identification code (usually using the "touch-tones" of a conventional telephone), and then dials the desired telephone number. Automated equipment reads the sequence of tones generated and if the identification number ("ID number") corresponds to a number validly issued to a subscriber, the proper telephone connection is made. The telephone call is then billed to the owner of the ID number used. Depending on what type of service is provided, the subscriber may be charged on a conventional time/distance basis for each telephone call, or the subscriber may be charged at a fixed monthly or other periodic rate.
A major convenience feature for subscribers is that any telephone within a service area (which, in some cases, includes the entire United States) can be used to make long distance calls for the cost of a local phone call, the long distance costs being charged to their separate account and billed later. Long distance calls can be made from public pay telephones without incurring operator assisted rates or requiring substantial amounts of change, and calls can be made by a subscriber from a third person's private or business phone without charging the third person's account.
A major disadvantage of using tone-based ID numbers is that anyone knowing or discovering a valid ID number can use that ID number to make telephone calls at either the service operator's or the subscriber's expense. Such fraudulent use of an ID number takes two predominant forms.
The first arises where the subscriber buys an unlimited amount of telephone time at a flat periodic rate. In this kind of arrangement, the service owner usually sets the flat rate according to a statistically calculated average amount of telephone use for a particular kind of subscriber and the service owners own cost for long distance lines. What often happens, however, is that the subscriber, since he is paying a fixed, flat rate, distributes the ID number to friends, family and acquaintances to allow them to use the subscriber's long distance service without charge. As a result, the amount of telephone usage that occurs on the subscriber's account is much greater than anticipated by the service owner, eroding the owner's profit or even forcing the owner to take a loss.
A second form of telephone ID number fraud occurs where a non-subscriber discovers a subscriber's ID number and uses that ID number to make telephone calls that are billed to the subscriber. Often a computer is used to generate and test different ID numbers until one or more numbers are found that gain access to the service. The subscriber is usually unaware that someone else is using the subscriber's number until the subscriber receives the resulting bill. By that time, the fraudulent user may have switched to a new ID number. If the fraudulent user uses public telephones to place the unauthorized calls, the fraudulent user can usually not be easily identified.
Several security access systems have been proposed to overcome the problem of unauthorized ID number use.
One such system involves the use of autodialers in which the ID number is not revealed to the user but is stored in the memory of an autodialer. To access the service, a subscriber holds the autodialer to the mouthpiece of a telephone and presses a button. The autodialer then emits the sequence of tones representing the subscriber's ID number. Although this security system makes it more difficult for a subscriber to share that subscriber's ID number with others, this security system can still be defeated by recording the tones on an ordinary cassette recorder and playing them back into a telephone. Alternatively, the autodialer can be played into any number of commercially available decoding devices to discover the ID number. Furthermore, use of an autodialer does not prevent the use of a computer to randomly generate numbers to discover operable ID numbers for fraudulent use.
A second security system makes use of tones that are not ordinarily found on conventional touch-tone telephones. The tones used on touch-tone telephones are standardized tones known as "Dual-Tone Multi-Frequency", or DTMF. The DTMF scale has 16 separate tones, only 12 of which can be generated by conventional telephones. By incorporating the additional tones in the ID number (and using an autodialer to produce the required tones), ordinary telephones can no longer be used for unauthorized access to the telephone service. However, the tones can still be tape recorded or generated by a computer.